Classifications

• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09D—COATING COMPOSITIONS, e.g. PAINTS, VARNISHES OR LACQUERS; FILLING PASTES; CHEMICAL PAINT OR INK REMOVERS; INKS; CORRECTING FLUIDS; WOODSTAINS; PASTES OR SOLIDS FOR COLOURING OR PRINTING; USE OF MATERIALS THEREFOR
  • C09D11/00—Inks
  • C09D11/02—Printing inks
  • C09D11/10—Printing inks based on artificial resins
  • C09D11/101—Inks specially adapted for printing processes involving curing by wave energy or particle radiation, e.g. with UV-curing following the printing
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
  • C08F20/00—Homopolymers and copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and only one being terminated by only one carboxyl radical or a salt, anhydride, ester, amide, imide or nitrile thereof
  • C08F20/02—Monocarboxylic acids having less than ten carbon atoms, Derivatives thereof
  • C08F20/10—Esters
  • C08F20/26—Esters containing oxygen in addition to the carboxy oxygen
  • C08F20/30—Esters containing oxygen in addition to the carboxy oxygen containing aromatic rings in the alcohol moiety
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
  • C08F290/00—Macromolecular compounds obtained by polymerising monomers on to polymers modified by introduction of aliphatic unsaturated end or side groups
  • C08F290/02—Macromolecular compounds obtained by polymerising monomers on to polymers modified by introduction of aliphatic unsaturated end or side groups on to polymers modified by introduction of unsaturated end groups
  • C08F290/06—Polymers provided for in subclass C08G
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
  • C08L63/00—Compositions of epoxy resins; Compositions of derivatives of epoxy resins
  • C08L63/10—Epoxy resins modified by unsaturated compounds
• • G—PHYSICS
  • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
  • G03F—PHOTOMECHANICAL PRODUCTION OF TEXTURED OR PATTERNED SURFACES, e.g. FOR PRINTING, FOR PROCESSING OF SEMICONDUCTOR DEVICES; MATERIALS THEREFOR; ORIGINALS THEREFOR; APPARATUS SPECIALLY ADAPTED THEREFOR
  • G03F7/00—Photomechanical, e.g. photolithographic, production of textured or patterned surfaces, e.g. printing surfaces; Materials therefor, e.g. comprising photoresists; Apparatus specially adapted therefor
  • G03F7/004—Photosensitive materials
  • G03F7/027—Non-macromolecular photopolymerisable compounds having carbon-to-carbon double bonds, e.g. ethylenic compounds
  • G03F7/032—Non-macromolecular photopolymerisable compounds having carbon-to-carbon double bonds, e.g. ethylenic compounds with binders
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
  • H01B3/00—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties
  • H01B3/18—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties mainly consisting of organic substances
  • H01B3/30—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties mainly consisting of organic substances plastics; resins; waxes
  • H01B3/44—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties mainly consisting of organic substances plastics; resins; waxes vinyl resins; acrylic resins
  • H01B3/443—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties mainly consisting of organic substances plastics; resins; waxes vinyl resins; acrylic resins from vinylhalogenides or other halogenoethylenic compounds
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
  • H01B3/00—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties
  • H01B3/18—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties mainly consisting of organic substances
  • H01B3/30—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties mainly consisting of organic substances plastics; resins; waxes
  • H01B3/44—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties mainly consisting of organic substances plastics; resins; waxes vinyl resins; acrylic resins
  • H01B3/447—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties mainly consisting of organic substances plastics; resins; waxes vinyl resins; acrylic resins from acrylic compounds
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
  • Y10T29/00—Metal working
  • Y10T29/49—Method of mechanical manufacture
  • Y10T29/4981—Utilizing transitory attached element or associated separate material
  • Y10T29/49812—Temporary protective coating, impregnation, or cast layer

Definitions

• This invention relates to a new and improved process for making protective coatings, such as solder mask coatings, its application to the preparation of printed circuits and the like, and improved photopolymerizable screen printing inks useful therefor. More specifically, the instant invention relates to liquid photopolymerizable compositions which may be readily applied by means of screen printing to a substrate and which are converted to dry, highly resistant coatings without the need to evaporate solvents and thermally cure.
• solder masks are generally used on quality printed circuit boards where molten solder is used to ensure good interconnections between the components and the circuitry.
• the solder masks must be extremely resistant to heat, impervious to a wide range of solvents, strongly adherent to a wide variety of metallic and non-metallic substrates, and chemically resistant to the commonly used rosin-based fluxes. Since solder masks are usually left on the circuitry as a protective coating, they must also have long term durability and excellent electrical insulating properties.
• solder mask coatings suffer from many disadvantages. Firstly, since they all contain significant amounts of solvents, drying of the freshly-printed coating consumes much time, requires significant heat energy, and generates solvent vapors which pollute the atmosphere. Additionally, the traditional solder mask coatings contain thermally-curable polymer systems such as epoxies or melamine-alkyds. These materials must be baked at temperatures of 120° to 175° C. for 30 to 60 minutes to effect the cure or cross-linking needed to give a resistant coating. Not only are energy and time consumed, but the baking process often liberates irritating and toxic fumes.
• a conductive circuit is built up from a bare plastic substrate by first using electroless plating to generate the conductive pattern.
• the resist coating on the substrate must endure electroless copper plating conditions, i.e., 30 minutes to 6 hours at pH 13 to 14 at temperatures of from 25° to 55° C. Very few coating materials are able to withstand such a treatment, and those coatings which do, generally require extensive baking periods prior to plating. Furthermore, since it is frequently desirable to leave such coatings on the printed circuit board, all-around durability and good electrical resistance are necessary.
• Silk screen printing has been used commercially for over 60 years. Basically, the technique involves squeezing ink through the open meshes of a stretched piece of fabric, originally made of silk, onto a printable substrate.
• the screen is imaged, i.e., covered or blocked out in part, by a masking material.
• the masking material may simply be a stencil or a dried lacquer, shellac or glue.
• activation may be adversely affected by the heat needed to laminate the photopolymerizable layer and by immersion in the developer solvent.
• the photopolymerizable layer is applied only at selected portions of the substrate. No material is wasted. The screen printing operation takes place at room temperature and there is no contact whatever with those portions of the substrate to be treated. Secondly, because none of the photopolymerizable material remains uncured, no development is required. Hence, this second source of possible damage to the pretreated substrate is avoided.
• the conventional photoresists whether liquid or dry-film, do not have the durability to perform as solder masks and cover coats.
• the screen-printable photopolymerizable coatings of the invention comprise the following essential components:
• a photopolymerizable material containing an aryloxyalkyl acrylate monomer or prepolymer (sometimes referred to herein as "epoxy-acrylates");
• compositions of the invention in contrast to the volatile solvent-containing screen printed coatings of the prior art is that the coatings are 100 percent solids (non-volatiles) before curing. Finer mesh sizes, therefore, can be used to get heavy coatings, thereby increasing the resolution capability. Reliable work with lines and spaces below 10 mils is possible. Additionally, because the inks can be left on the screen indefinitely without any hardening or thickening, it is unnecessary to clean up the screens during short periods of inactivity. Also, time and energy are saved because curing of the material can be accomplished in exposure times of less than 5 seconds. Elimination of the drying time saves up to 90 percent of the electrical energy, since ultra-violet curing replaces the infra-red drying.
• the photopolymerizable compositions contain the following proportions of the essential components:
• the aryloxyalkyl acrylate monomers and prepolymers of the invention are the reaction products of epoxy compounds or omega-hydroxy ethers and unsaturated carboxylic acids.
• the carboxylic acids may be mono- or dicarboxylic acids containing from 3 to 18 carbon atoms. Alpha, beta-unsaturated carboxylic acids such as acrylic and methacrylic acids are preferred.
• Monomers and prepolymers of the above type are commercially available under the tradenames of "Epocryl” (Shell Chemical Company), “Derakane” (Dow Chemical Company), “Nupol” (Freeman Chemical Company), and SR-348 and SR-349 (Sartomer Resins Company).
• aryloxyalkyl acrylates can be described as having the following general formula: ##STR1## wherein X may be a methylene, an alkyl-substituted methylene group, a dialkyl-substituted methylene group, a carbonyl group, a sulfide, a sulfoxide, a sulfone, an amine, an alkyl-substituted amine, an ethylene ether, a propylene ether, a 2-hydroxypropylene ether, wherein each alkyl group may have from 1 to 8 carbon atoms, or any combination thereof; Y may be ethyl, propyl, 2-hydroxypropyl, or other lower alkyl or hydroxyalkyl groups having up to 8 carbon atoms; A may be an unsaturated acyloxy group having from 3 to 18 carbons, preferably acryloxy or methacryloxy; and n may be 0 through 20, m may be 0 or 1, and
• aromatic rings shown in the formula may be ring-substituted with 1 to 4 additional substituents such as chlorine or bromine.
• the photopolymerizable diluents of the invention are ethylenically unsaturated compounds which contain at least one terminal ethylenic group. It is most preferable that at least two or more terminal ethylenic groups be present.
• the diluent must have a boiling point of at least 100° C. at atmospheric pressure and be capable of forming a high polymer by free-radical photo-initiated chain-propagating addition-polymerization.
• esters of polyols particularly such esters of the methylene carboxylic acids, e.g., ethylene diacrylate; diethylene glycol diacrylate; glycerol diacrylate; glycerol triacrylate; ethylene dimethacrylate; 1,3-propylene dimethacrylate; 1,2,4-butanetriol trimethacrylate; 1,4-benzenediol dimethacrylate; pentaerythritol tetramethacrylate; 1,3-propanediol diacrylate; 1,6-hexanediol diacrylate; the bis-acrylates and methacrylates of polyethylene glycols of molecular weight 200-500; trimethylolpropane triacrylate; pentaerythritol triacrylate; unsaturated amides, particularly those of the methylene carboxylic acids, and especially those of alpha,omega-diamines and oxygen-interrupted omega-di
• Monofunctional monomers may also be used as polymerizable diluents, but these are generally less satisfactory because of greater volatility and because they tend to form less durable polymers. These materials include hydroxyalkyl acrylates and methacrylates, dibromopropyl acrylate and methacrylate, and the half-esters of hydroxyalkyl acrylates and methacrylates with such dicarboxylic acids as maleic, adipic, and phthalic acid.
• the photo-initiators used in the compositions are preferably those activatable by actinic light and thermally inactive at 185° C. and below.
• the amount used in the composition varies widely depending on the initiator selected. The optimum amount, however, can be readily determined by simple experimentation.
• the most preferred initiators are the acyloin ethers such as the benzoin ethers, particularly benzoin isobutyl ether, alkyl-substituted antraquinones such as 2-tert-butylanthraquinone, and ⁇ , ⁇ -diethoxyacetophenone.
• initiators which may be used include the substituted or unsubstituted polynuclear quinones, such as 9,10-anthraquinone; 1-chloroanthraquinone; 2-chloroanthraquinone, 2-methylanthraquinone; 2-ethylantraquinone; octamethylanthraquinone; 1,4-naphthoquinone; 9,10-phenanthraquinone; 1,2-benzanthraquinone; 2,3-benzanthraquinone; 2-methyl-1,4-naphthoquinone; 2,3-dichloronaphthoquinone; 1,4-dimethylanthraquinone; 2,3-dimethylanthraquinone; 2-phenylanthraquinone, 2,3-diphenylanthraquinone; sodium salt of anthraquinone alpha-sulfonic acid; 3-chloro-2
• photoinitiators described in U.S. Pat. No. 2,760,863, some of which may be thermally active at temperatures as low as 85° C., are also useful: vicinal ketaldonyl compounds, such as diacetyl and benzil; alpha-ketaldonyl alcohols, such as benzoin and pivaloin; alpha-hydrocarbon-substituted aromatic acyloins; alpha-methylbenzoin; alpha-allylbenzoin; and alpha-phenylbenzoin.
• vicinal ketaldonyl compounds such as diacetyl and benzil
• alpha-ketaldonyl alcohols such as benzoin and pivaloin
• alpha-hydrocarbon-substituted aromatic acyloins alpha-methylbenzoin
• alpha-allylbenzoin alpha-phenylbenzoin
• Silver persulfate is also useful as a free-radical generating initiator activatable by actinic radiation.
• Certain aromatic ketones e.g., benzophenone and 4,4'-bis-dialkylaminobenzophenones, are also useful.
• the photopolymerizable compositions may contain, in addition to those set forth in Table A, the following proportions of the several components:
• the materials of the invention are resistant to high temperatures, remain flexible after exposure to high temperature, have good dielectric properties, viz., an insulation resistance of 1 ⁇ 10 11 ohms or higher, low permeability to both air and moisture, and adhere to a broad cross-section of materials such as various metals and plastic compositions.
• the high temperature resistance makes the coating particularly useful for reflowing low melting (225°-350° C.) metals for leveling and for alloying bimetals such as deposited in tin-lead electroplating.
• the solvent resistance of the coatings of the invention is outstanding. For example, they are able to withstand immersion in 3 percent potassium hydroxide or methylene chloride for 4 hours at room temperature. Furthermore, high temperature immersion at 55° C. in 3 percent potassium hydroxide for over 1 hour results in no degradation.
• the coating can be removed only by the most potent solvent blends such as those used for stripping baked epoxides.
• Thermal polymerization inhibitors are generally also present in the preferred compositions. These materials act as antioxidants and stabilizers and include p-methoxyphenol, hydroquinone and alkyl and aryl-substituted hydroquinones and quinones, tert-butyl catechol, pyrogallol, copper resinate, napthylamines, beta-naphthol, cuprous chloride, 2,6-di-tert-butyl p-cresol, 2,2-methylenebis-(4-ethyl-6-t-butylphenol), phenothiazine, pyridine, nitrobenzene, dinitrobenzene, p-toluquinone, chloranil, aryl phosphites, and aryl alkyl phosphites.
• composition of the invention In order to obtain a useful screen printing coating, it is essential that the composition of the invention have the appropriate viscosity and thixotropic properties. While usable compositions may be obtained by the selection of the epoxy-acrylates and the photopolymerizable diluents in the relative amounts thereof employed, it is generally desirable to add thixotropic agents, leveling agents and defoamers to achieve a viscosity of from 5,000 to 200,000 centipoises and a thixotropic index of from 1.00 to 6.00.
• thixotropic agents which may be used are well known to those skilled in the art. Examples of these materials are Bentone (a trademark of National Lead Company for an organic base salt of a clay mineral, e.g., montmorillonite) and other silicate-type materials. Other thixotropic agents are the aluminum, calcium, and zinc salts of fatty acids, such as lauric or stearic acid, e.g., Zinc Soap No. 26 (trademark of the Witco Chemical Co., Inc.); and fumed silicas such as Cab-o-Sil and Santocel (trademarks of the Cabot Corporation and Monsanto Corporation, respectively).
• Bentone a trademark of National Lead Company for an organic base salt of a clay mineral, e.g., montmorillonite
• Other thixotropic agents are the aluminum, calcium, and zinc salts of fatty acids, such as lauric or stearic acid, e.g., Zinc Soap No. 26 (trademark of the Wit
• the leveling agents and defoamers which may be used include Modaflow and Multiflow. These are trademarks of the Monsanto Company for resin modifiers.
• Other leveling and flowout agents include aluminum stearate, calcium stearate, sucrose benzoate, and high molecular weight nonionic surface active agents.
• ingredients may also be added to the coatings of the invention. These include plasticizers, pigments or colorants, fillers, and adhesion promoters. Those skilled in the art may readily determine the amount of such materials desirable.
• Suitable plasticizers used to increase the flexibility of the film, include the polyfunctional esters such as dioctyl phthalate, tricresyl phosphate, polyethyleneglycol diacetate, and pentaerythritol tetramercaptopropionate.
• any of the well known screen printing techniques may be employed.
• the photopolymerizable ink is applied by pouring a measured quantity on the screen.
• the squeegee is drawn uniformly and with even pressure to scrape the ink across the entire surface of the screen, thereby transferring the ink to the substrate below. Thereafter, the screen is lifted and the substrate removed.
• Film thicknesses ranging from 0.006 mm. to 0.130 mm. are applied by this procedure. Film thickness can be measured by such means as micrometer or beta-ray back-scattering.
• the screen is lifted and the wet substrate removed and passed to the ultraviolet radiation source.
• ultraviolet radiation sources include carbon arcs, mercury vapor lamps, fluorescent lamps with ultraviolet radiation-emitting phosphors, argon glow lamps, electronic flash units and photographic flood lamps.
• the medium pressure mercury vapor lamps are the most suitable.
• the period of exposure will be dependent on the film thickness, the light intensity, the distance from the light source to the ink and the temperature of the operation. A typical exposure time using a 200 watt per linear inch medium pressure mercury vapor lamp at a distance of 4 inches is about 5 seconds.
• the ink is completely cured and may be passed directly to the next processing step to modify the unexposed portion of the substrate.
• the photopolymerizable compositions of the invention make possible processing sequences not heretofore feasible.
• the sequence would be: (1) activate the substrate; (2) form the electroless copper deposit; (3) apply the photopolymerizable film over the electroless copper layer; (4) expose the film through a negative; (5) develop by washing away the unpolymerized areas; (6) electroplate the exposed areas; (7) strip the resist; and (8) dissolve the uncoated electroless copper. Contrast this to the improved process of the instant invention.
• the substrate as for example an epoxy-fiberglass board, is first activated; the photopolymerizable ink is applied imagewise via a screen printing process; the wet ink is instantly cured without the need for developing; and thereafter the electroless copper layer is deposited, followed by the electroplating.
• Thi sequence of steps eliminates the development step, the stripping of the resist, and the need to dissolve the extraneous electroless copper. It is necessary to dissolve the electroless copper coating in the process of the prior art, since obviously this conductive surface would destroy the usability of the printed circuit board. From the material standpoint, no more photopolymer is required than that needed to form the resist and no more electroless copper employed than needed to coat the area intended to be plated.
• a photopolymerizable screen-printable ink composition useful for solder mask applications is prepared having the following composition:
• a copper-clad epoxy-fiberglass printed circuit board having an etched conductive pattern is used as the test panel.
• the panel is placed under a silk screen frame having a patterned screen tautly stretched within.
• a measured amount on the photopolymerizable composition is poured onto the screen, and the composition is screen-printed onto the test panel uniformly with a squeegee using methods well known to those skilled in the art. Observation of the application shows that the polymerizable composition covers the surface uniformly, even though the panel surface is not planar, forming a layer about 1 mil in thickness.
• the screen is removed from the substrate. There is no mesh marks on the printed substrate and the design on the screen is reproduced with excellent integrity.
• the substrate containing the wet photopolymerizable coating is exposed for 5 seconds to a 200 watt per linear inch medium pressure mercury vapor lamp at a distance of 4 inches. After the exposure, the printed coating is completely hardened to form a solder mask resist.
• the cured coating is a tough thermoset-like material which cannot be manually scratched or chipped.
• the cured coating has an insulation resistance of 1.2 ⁇ 10 12 ohms as determined by MIL-I-46058C, a value which is considered to be excellent by known standards.
• the panel is then subjected to wave-soldering at 260° C.
• wave-soldering is well known to those in the art, being performed on a machine such as the Gale AA-11 manufactured by Excellon Industries.
• the panel passes through the machine on a conveyor and is treated in three steps: (1) foam fluxing, to prepare the exposed copper for good solder adhesion; (2) preheating to drive off the flux solvents, activate the flux and reduce the thermal shock of the board contacting molten solder; and (3) wave soldering, where the inverted board is passed over a 3 inch wide wave of molten solder at a conveyor speed of 18 inches per minute, to deposit a uniform layer of solder upon the exposed copper surfaces and in all through-hole connections.
• the panel is then cooled with air or water spray and treated with a flux-removing solvent such as methylene chloride, and dried. Examination of the panel shows that the coating has completely protected the covered areas from solder. The coating remains hard and durable, thus giving the covered areas a permanent protection for the life of the circuit board.
• a flux-removing solvent such as methylene chloride
• a photopolymerizable screen-printable ink composition useful for solder mask and additive circuitry applications is prepared having the following composition:
• An epoxy-fiberglass composite board is palladium-activated with a solution described in U.S. Pat. No. 3,011,920 to Shipley.
• the sensitized board is screen printed with the above formulation as described in Example I.
• the ink has a viscosity of 100,000 cenipoises and a thixotropic index of 3.31.
• the photopolymerizable composition covers the surface uniformly and no mesh marks appear on the substrate. The design on the screen is reproduced with excellent integrity.
• the wet photopolymerizable ink is cured by exposure as described in Example I. After exposure, the printing coating is completely hardened.
• the board thus prepared is treated sequentially with the electroless copper plating bath, the copper sulfate electroplating bath and the tin-lead fluoborate electroplating bath.
• the three treating steps may be described as follows:
• Electroless copper plating bath This bath contains 9.25 grams per liter of copper sulfate, 16 grams per liter of sodium hydroxide, 5 grams per liter of sodium carbonate, 30 grams per liter of 37 percent formaldehyde and 33 grams per liter of a chelating agent. It has a pH of 13.3. The board is subjected to immersion in this bath for 10 minutes at 25° C. The use of this bath is further described in U.S. Pat. No. 3,790,392 to Gilano.
• Copper sulfate electroplating bath This bath contains 120 grams per liter of copper sulfate, 215 grams per liter of sulfuric acid, and 40 grams per liter of brightener and has a pH of 0.2. The board is subjected to immersion in this bath for 30 minutes at 25° C. with an applied current of 30 amperes per square foot.
• Tin-lead (60/40) fluoborate electroplating bath This bath contains 52 grams per liter of stannous ion, 30 grams per liter of lead ion, 100 grams per liter of fluoboric acid, 25 grams per liter of boric acid and 5 grams per liter of peptone. The pH is 0.2. The board is subjected to immersion in this bath for 15 minutes at 25° C. with an applied current of 15 amperes per square foot.
• the resist After the substrate is removed from the final bath, the resist is carefully inspected. Inspection shows that the resist is intact, and still substantially similar in appearance to the resist prior to the treating operations.
• the resist has an insulation resistance of 1.2 ⁇ 10 12 ohms.
• the cured formulation of this example can be wave soldered, as described in Example I, without detriment.
• a photopolymerizable screen-printable ink composition useful for solder mask and additive circuitry applications is prepared having the following compositon:
• a copper-clad epoxy-fiberglass printed circuit board is coated with photoresist, exposed through a photographic negative and developed according to the procedure described in the Celeste patent.
• the unprotected copper surface is then pattern-plated successively in the copper sulfate electroplating bath and a tin-lead fluoborate electroplating bath, described in Example II.
• Deposits of approximately 1 mil each of electroplated copper and tin-lead are built up over the exposed sections of copper foil.
• the photoresist is stripped, and the panel is subjected to a spray of Alkaline Etchant A system (manufactured by Southern California Chemical Company) for 3 to 5 minutes at 55° C. (cf. U.S. Pat. No. 3,705,061 to King).
• the electroplated tin-lead layer acts as an etch resist, and the unprotected copper foil is dissolved. Following this etching process, there remains a circuit pattern composed of three layers, i.e., copper foil, electroplated copper, and electroplated tin-lead.
• the panel is then subjected to a process called "solder reflow.”
• the electroplated tin-lead bimetallic deposit is fused to form the solder alloy. This improved the conductivity, physical properties and corrosion-resistance of the tin-lead deposit.
• the composition of Table III is applied and cured as described in Example I.
• the ink has a viscosity of 6500 centipoises and a thixotropic index of 1.30.
• the panel is then immersed in heated oil at a temperature of 245° to 275° C. for 10 to 20 seconds. During this brief period the reflow process takes place and the alloy forms.
• the panel is cooled, cleaned with chlorinated solvent to remove the oil, and dried. Examination of the panel shows that the cured coating is intact. The coating remains on the panel as permanent protection for the life of the circuit board. This coating has an insulation resistance of 1.8 ⁇ 10 12 ohms.
• the cured formulation of this example can be wave soldered, as described in Example I, without detriment.
• a photopolymerizable screen-printing ink composition useful for solder mask and additive circuitry applications is prepared having the following composition:

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• Inks, Pencil-Leads, Or Crayons (AREA)
• Non-Metallic Protective Coatings For Printed Circuits (AREA)
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• 1974
  • 1974-05-24 US US05/473,180 patent/US4003877A/en not_active Expired - Lifetime
• 1975
  • 1975-05-12 ZA ZA00753049A patent/ZA753049B/xx unknown
  • 1975-05-14 GB GB20460/75A patent/GB1507842A/en not_active Expired
  • 1975-05-14 IN IN963/CAL/75A patent/IN142791B/en unknown
  • 1975-05-18 IL IL47310A patent/IL47310A/xx unknown
  • 1975-05-20 FI FI751475A patent/FI59112C/fi not_active IP Right Cessation
  • 1975-05-21 ES ES437825A patent/ES437825A1/es not_active Expired
  • 1975-05-21 IT IT49715/75A patent/IT1035820B/it active
  • 1975-05-22 DD DD191378A patent/DD124390A5/xx unknown
  • 1975-05-22 SE SE7505838A patent/SE431879B/xx unknown
  • 1975-05-22 DD DD186195A patent/DD120662A5/xx unknown
  • 1975-05-23 FR FR7516148A patent/FR2274652A1/fr active Granted
  • 1975-05-23 BE BE156665A patent/BE829437A/xx not_active IP Right Cessation
  • 1975-05-23 DK DK227875A patent/DK154919C/da not_active IP Right Cessation
  • 1975-05-23 NL NLAANVRAGE7506080,A patent/NL173178B/xx not_active Application Discontinuation
  • 1975-05-23 BG BG030068A patent/BG26402A3/xx unknown
  • 1975-05-23 AR AR258934A patent/AR217039A1/es active
  • 1975-05-23 BR BR4189/75A patent/BR7503276A/pt unknown
  • 1975-05-23 DE DE2522811A patent/DE2522811C2/de not_active Expired
  • 1975-05-23 CA CA227,687A patent/CA1049691A/en not_active Expired
  • 1975-05-23 RO RO7582318A patent/RO67457A/ro unknown
  • 1975-05-23 CH CH756624A patent/CH608825A5/xx not_active IP Right Cessation
  • 1975-05-23 NO NO751830A patent/NO146676C/no unknown
  • 1975-05-24 JP JP50062416A patent/JPS515388A/ja active Pending
  • 1975-05-26 AT AT400775A patent/AT339928B/de not_active IP Right Cessation
• 1976
  • 1976-06-01 US US05/691,922 patent/US4064287A/en not_active Expired - Lifetime

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